FIG. 9 schematically shows an example of a conventional superconducting wire in cross-section. The conventional superconducting wire has a structure in which an intermediate layer 2 composed of cerium oxide or yttria-stabilized-zirconia, for example, a superconducting layer 3 composed of an oxide superconductor of a Ho—Ba—Cu—O system or a Y—Ba—Cu—O system, for example, and a silver stabilization layer 4 serving as a stabilization layer for superconducting layer 3 and composed of silver are successively laid on a substrate 1 composed of a Ni alloy and the like (for example, see FIG. 1 of Japanese Patent Laying-Open No. 07-37444 (Patent Document 1)).
In the above-mentioned conventional superconducting wire, variation in the amount of oxygen in the oxide superconductor forming superconducting layer 3 significantly changes characteristics of superconducting layer 3. Therefore, it is common to adjust the amount of oxygen in the oxide superconductor forming superconducting layer 3 by performing heat treatment after silver stabilization layer 4 is formed on superconducting layer 3.
There is a problem, however, that the fabrication cost is increased if a large amount of silver is used to form silver stabilization layer 4 since silver is a relatively expensive material for an industrial material. In addition, there is also a problem that the superconducting wire cannot obtain enough mechanical strength if silver stabilization layer 4 is employed.
In order to solve such problems, there has been proposed a method to affix copper foil uniformly onto superconducting layer 3 of a superconducting wire in a longitudinal direction by soldering.    Patent Document 1: Japanese Patent Laying-Open No. 07-37444